The present invention relates to cold-water responsive compositions and methods of manufacturing and using cold-water responsive compositions. The cold-water responsive compositions of the present invention have a wide range of cold-water responsiveness ranging from cold-water dispersible to cold-water weakenable. The cold-water responsive compositions of the present invention comprise a blend of a hydrolytically degradable polymer such as polylactic acid and at least one cold-water responsive polymer such as polyvinyl alcohol. The compositions of the present invention are responsive to water at ambient temperature and conditions are particularly suited for use in the manufacture of a variety of disposable products.
Even though the amount of plastics used in a variety of consumer goods, packaging and medical articles has not significantly increased over the past twenty years, the common perception is that more and more plastics are filling up our landfills. Plastics offer many advantages over the more traditional wood, glass, paper, and metal articles including improved performance, comparable or decreased cost of manufacture and decreased transportation costs. Disposal of all waste materials, including food waste, packaging materials, medical waste into a typical landfill provides a relatively stable environment in which none of these materials is seen to decompose at an appreciable rate. Alternative waste disposal options are increasingly discussed and utilized to divert some fractions of waste from entombment. Examples of these alternatives include municipal solid waste composting, anaerobic digestion, enzymatic digestion, and waste water sewage treatment.
Much controversy is associated with the disposal of medical waste. Both government agencies and members of the public sector have been increasingly directing in-depth scrutiny toward this subject. Admittedly, concerns over the fate of materials contaminated with infectious substances are valid and proper measures to insure the safety of health care workers and the general public should be taken.
Currently, medical waste can be categorized into reusable and disposable. Categorization as to whether certain waste is reusable or disposable is customarily determined according to the material from which the article was constructed and the purpose for which the article was used.
After use, reusable medical articles are cleansed and sterilized under stringent conditions to ensure disinfection. In comparison, disposable medical articles are usually only used once, and even then, disposing procedures are not straightforward, rather they often involve several steps to safeguard against potential hazards. Typically, after use, disposable medical articles must be disinfected or sterilized, adding a significant cost prior to disposal into a specially designated landfill or waste incinerator. As a result, the disposal cost for the contaminated single use articles is quite high.
Despite the high cost of disposal, single use medical articles are desirable because of the assurance of clean, and uncontaminated equipment. Many times in the medical context, sterilization procedures conducted improperly can result in detrimental effects such as the transmission of infectious agents from one patient to another. Improper sterilization can also be disastrous in a laboratory setting, where, for example, contaminated equipment can ruin experiments resulting in tremendous costs of time and money.
Currently, disposable medical fabrics are generally composed of thermoplastic fibers such as polyethylene, polypropylene, polyesters, polyamides and acrylics. They are typically from 10 to 100 grams per square yard in weight and can be woven, knitted or otherwise formed by methods well known to those in the textile arts while the non-wovens can be thermobonded, hydroentangled, wet laid or needle punched and films can be formed by blow or cast extrusion or by solution casting.
The use of polymers for various disposable articles is widespread and well known in the art, In fact the heaviest use of polymers in the form of film and fibers occurs in the packaging and disposable article industries. Films and fibers employed in the packaging industry include those used in food and non-food packaging, merchandise bags and trash bags. In the disposable article industry, the general uses of polymers occurs in the construction of diapers, personal hygiene articles, surgical drapes and hospital gowns, instrument pads, bandages, and protective covers for various objects.
In light of depleting landfill space and inadequate disposal sites, there is a need for polymers, which are water responsive. Currently, although polymers such as polyethylene, polypropylene, polyethylene terephthlate, nylon, polystyrene, polyvinyl chloride and polyvinyldene chloride are popular for their superior extrusion and film and fiber making properties, these polymers are not water responsive. Furthermore, these polymers are generally non-compostable, which is undesirable from an environmental perspective.
Polymers and polymer blends have been developed which are generally considered to be water responsive. These are polymers, which purportedly have adequate properties to permit them to breakdown when exposed to conditions, which lead to composting. Examples of such arguably water responsive polymers include those made from polyethylene oxide, starch biopolymers and polyvinyl alcohol.
Although polymers extruded from these materials have been employed in film and fiber containing articles, many problems have been encountered with their use. Often the polymers are not completely water responsive or compostable. Furthermore, some water responsive polymers may also be unduly sensitive to water, either limiting the use of the polymer or requiring some type of surface treatment to the polymer, often rendering the polymer non-water responsive. Other polymers are undesirable because they have inadequate heat resistance for wide spread use.
Personal care products such as diapers, sanitary napkins, adult incontinence garments, and the like are generally constructed from a number of different components and materials. Such articles usually have some portion, usually the backing layer, constructed of a liquid repellent or non-water responsive polymer material. The non-water responsive material commonly used includes plastic materials such as polyethylene film or copolymers of ethylene and other polar and nonpolar monomers. The purpose of the non-water responsive layer is to minimize or prevent absorbed liquid that may, during use, exude from the absorbent and soil the user or adjacent clothing. The non-water responsive layer also has the advantage of allowing greater utilization of the absorbent capacity of the product.
Although such products are relatively inexpensive, sanitary and easy to use, disposal of a soiled product is not without its problems. Typically, the soiled products are disposed in a solid waste receptacle. This adds to solid waste disposal costs and presents health risks to persons who may come in contact with the soiled product. An ideal disposal alternative would be to use municipal sewage treatment and private residential septic systems by flushing the soiled product in a toilet. Products suited for disposal in sewage systems are termed xe2x80x9cflushable.xe2x80x9d While flushing such articles would be convenient, the non-water responsive material currently used in personal care products normally does not disintegrate in water. This tends to plug toilets and sewer pipes, frequently necessitating a visit from a plumber. At the municipal sewage treatment plant, the non-water responsive material may disrupt operations by plugging screens and causing sewage disposal problems. It therefore becomes necessary, although undesirable, to separate the barrier film material from the absorbent article prior to flushing.
In addition to the article itself, typically the packaging in which the disposable article is distributed is also made from a non-water responsive, specifically water resistant, material. Water resistivity is necessary to prevent the degradation of the packaging from environmental conditions and to protect the disposable articles therein. Although this packaging may be safely stored with other refuse for commercial disposal, and especially in the case of individual packaging of the products, it is often more convenient to dispose of the packaging in the toilet with the discarded disposable article. However, where such packaging is composed of a water resistant material, the aforementioned problems persist.
The use of lactic acid and lactide to manufacture a water responsive polymer is well known in the medical industry. Such polymers have been used in the past for making sutures, clamps, bone plates and biologically active controlled release devices. Processes developed for the manufacture of such polymers to be utilized in the medical industry have incorporated techniques, which respond to the need for high purity and biocompatibility in the final product. These processes, however, are typically designed to produce small volumes of high dollar-value products, with less emphasis on manufacturing cost and yield.
It is generally known that lactide polymers or poly(lactides) are unstable, however, the consequence of this instability has several aspects. One aspect is biodegradation or hydrolysis, which occurs when lactide polymers, or articles manufactured from lactide polymers, are discarded or composted after completing their useful life. Another aspect of such instability is the degradation of lactide polymers during processing at elevated temperatures as, for example, during melt processing by end-user purchasers of polymer resins.
In the medical area there is a predominant need for polymers which are highly stable and therefore desirable for use in medical devices. Such a demand has historically been prevalent in the high value, low volume medical specialty market, but is now also equally prevalent in the low value, high volume medical market.
As described in U.S. Pat. No. 5,472,518, compositions comprised of multilayer polymer films are known in the art. The utility of such structures lies in the manipulation of physical properties in order to increase the stability or lifetime during use of such structure. For example U.S. Pat. No. 4,826,493 describes the use of a thin layer of hydroxybutyrate polymer as a component of a multilayer structure as a barrier film for diaper components and ostomy bags.
Another example of use of multilayer films is found in U.S. Pat. No. 4,620,999 which describes the use of a water soluble film coated with, or laminated to, a water insoluble film as a disposable bag. The patent describes a package for body waste which is stable to human waste during use, but which can be made to degrade in the toilet, at a rate suitable for entry into a sewage system without blockage, by adding a caustic substance to achieve a pH level of at least 12. Such structures usually consist of a polyvinyl alcohol film layer coated with polyhydroxybutryate.
A similar excretion-treating bag allowing discarding in flush toilet or sludge vessel is disclosed in JP 6142127. It is composed of an inner layer of water resistant resin such as polylactide and an outer layer of water soluble polyvinyl alcohol. As disclosed in this patent, there are many examples of multilayer films that are utilized in disposable objects. Most of these examples consist of films or fibers, which are comprised of external layers of an environmentally degradable polymer and an internal layer of water responsive polymer. Typically, the external layers are comprised of polyolefin, polycaprolactone, or ethylene vinyl acetate and the internal layer is comprised of polyvinyl alcohol. These examples, however, are all limited to compositions consisting of multilayers of different polymers, and do not encompass actual blends of different polymers.
Another family of patents, including EP 241178, JP 62223112, and U.S. Pat. No. 4,933,182, describes a controlled release composition for treating periodontal disease. The compositions are comprised of a therapeutically effective agent in a two-phase carrier consisting of a continuous phase and a discontinuous phase. The continuous phase consists of a water soluble polymer and the discontinuous phase consists of a polymer of limited water solubility. Although the compositions of these inventions include the use of more than one polymer, the polymers are utilized in layers and not as intermingled or blended components.
The use of polymer blends for use in water responsive articles is also disclosed in U.S. Pat. Nos. 5,508,101, 5,567,510, and 5,472,518. This group of patents describes compositions that are designed to be sturdy and resistant to water during storage, preparation and use but dispersible in a commercial laundry cycle. Specifically, the compositions described in the above group of patents are aqueous-alkali dispersible. More specifically, the compositions described in the above group of patents are dispersible in water at conditions of elevated temperature, greater than 50xc2x0 C., and elevated pH, greater than 7. These compositions dispersed via hydrolytical degradation of the hydrolytically degradable polymer under the specific conditions encountered during a commercial laundry cycle. The compositions described in the above group of patents are not dispersible in cold water and do no lose their integrity when in contact with tap water for more than twenty-four hours. Therefore, there is a need to provide compositions that are at least weakenable, preferably, disintegratable and more preferably, dispersible in ordinary tap water without elevated temperature, without elevated pH and without a laundry cycle.
Further, the compositions of this group consist of articles constructed from polymers, which are first formed into fibers or films and then combined. As such, the compositions are actually mini-layers of the individual polymer films or fibers. Therefore, although the fibers and films of the polymers of such compositions are considered to be in very close proximity with one another, they are not actual polymer blends made by melting the polymers into a homogenous molten mixture. The dispersion of one polymer within another in these compositions, is not viewed as homogenous since the individual polymers are essentially distinct and separate fibers or films.
Polymer blend compositions consisting of fibers and films that are optimally combined are desirable because they are highly stable. Optimal combination of polymers means the polymers of the blend are connected as closely as possible without the requirement of polymerization. Although blended polymer compositions are known, improved polymer blends wherein the fibers and films are more intimately connected are desirable since the resulting composition is then more stable, pliable and versatile.
In addition to the need for polymer compositions that are highly stable, and therefore suitable for regular use in most disposable articles, there is a simultaneous need for such polymer compositions to be cold-water responsive. What is needed therefore, is a material that may be utilized for the manufacture of disposable articles and which is cold-water responsive. Desirably, such a material should be versatile and inexpensive to produce. Additionally, the material should be stable enough for intended use but subject to degradation under predetermined conditions.
The present invention provides selectively cold-water responsive compositions made from polymers such as polylactide and cold-water soluble polyvinyl alcohol. The present invention also provides methods of making and using cold-water responsive compositions and includes articles comprising the cold-water responsive compositions. Desirably, the articles are designed for a single use and are disposable in cold water by flushing in a toilet.
Products used according to the present invention comprise cold-water responsive polymer compositions. The term xe2x80x9ccold-water responsive,xe2x80x9d as used herein, means that the compositions are either cold-water dispersible, cold-water disintegratable or cold-water weakenable. The degree of cold-water responsiveness may vary depending upon the composition of the polymers, chemical or manufacturing modifications thereto, and the temperature of the water, for example. The compositions of the present invention do not disperse via hydrolytical degradation of a hydrolytically degradable polymer, for example polylactide. The compositions of the present invention are responsive to cold water by the gradual dissolution of a cold-water soluble component in the compositions, for example cold-water soluble polyvinyl alcohol.
Products of the present invention may be constructed of combinations of polymers including, but not limited to: polylactic acid, polyvinyl alcohol, polycapralactone polyhydroxybutryate-co-valorate, polyethylene succinate and polybutylene succinate. A commercial example of polybutylene succinate is sold under the trademark BIONOLLE(copyright). Products of the present invention are constructed of compositions comprising at least one hydrolytically degradable polymer and at least one cold-water soluble polymer. The term xe2x80x9chydrolytically degradable,xe2x80x9d as used herein, means degradation by hydrolysis. Hydrolytically degradable polymers include, but are not limited to, polylactic acid, polyester amides, polyglycolic acid, and polyhydroxybutyrate-co-valorate and the like; and combinations thereof as copolymers, blends, mixtures and the like. The term xe2x80x9ccold-water soluble,xe2x80x9d as used herein, means that the polymer will completely dissolve upon extended contact with cold water at temperatures less than about 45xc2x0 C., preferably at temperatures less than about 25xc2x0 C. Nonlimiting types of water soluble polymers include polyvinyl alcohol, polyaspartic acid, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyvinyl pyrrolidone, polyalkylene oxides, complex carbohydrates and combinations thereof as copolymers, blends, mixtures, and the like.
The present invention discloses selectively cold-water responsive polymer blend compositions of films and fibers having a wide range of cold-water responsiveness including water dispersible, water disintegratable, water weakenable and water stable. The present invention also discloses methods for the manufacture of cold-water responsive polymer blend compositions useful for manufacturing films and fibers to suit for different application needs. The composition range responsible for each type of water responsiveness is also disclosed. The compositions of the present invention are useful as components in flushable personal care products, such as the outer cover film for diapers, the laminating film for clothlike outer cover, baffle film for feminine pads and pantiliners, etc. In addition to flushability, the compositions of the present invention have the advantage of being biodegradable so that the materials will degrade in anaerobic digesters and aeration tanks in wastewater treatment plants and will not increase the volume of sludge.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments.